Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754364AbbKWRgr (ORCPT ); Mon, 23 Nov 2015 12:36:47 -0500 Received: from mail-wm0-f52.google.com ([74.125.82.52]:37256 "EHLO mail-wm0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750976AbbKWRgp (ORCPT ); Mon, 23 Nov 2015 12:36:45 -0500 MIME-Version: 1.0 In-Reply-To: References: <1447960147-2681-1-git-send-email-brianrob@microsoft.com> <20151119193101.GQ3816@twins.programming.kicks-ass.net> <20151120193217.GW3816@twins.programming.kicks-ass.net> Date: Mon, 23 Nov 2015 09:36:44 -0800 Message-ID: Subject: Re: [PATCH] perf: Fallback to JIT support for mmap'd non-ELF binaries. From: Stephane Eranian To: Brian Robbins Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2708 Lines: 64 On Fri, Nov 20, 2015 at 1:18 PM, Brian Robbins wrote: > > > On Fri, 20 Nov 2015, Peter Zijlstra wrote: > >> On Thu, Nov 19, 2015 at 11:45:45PM +0000, Brian Robbins wrote: >> >> > Thank you for the feedback. The file format is similar to PE, but is >> > not identical. So, we would be implementing something very scoped, >> > which doesn't feel right to me. >> >> *groan* you just had to go and invent yet another executable format, >> right? :-) > Nah, it just has some extra stuff in it that makes this less desirable - > it's technically PE, but anyway. >> >> > I am interested in the new JIT support, however my understanding from >> > the information that I've read is that it requires kernel support in >> > 4.x, though I can't seem to find where I read that. I want to make >> > sure that this works on older kernels (3.x) as well. >> >> As I think Stephane explained, this is only required if you need to >> match up kernel and userspace timestamps, which is important for dynamic >> code generation, less so for static code in a weird format. > > Yes, agreed. > >> >> So what the new JIT stuff does is online write 'fake' ELF files with >> symbol sections and (optionally?) dwarf debug info for line numbers. >> The debug info section is optional and contains the line table info. This can be used should you want to display source code along with assembly. >> Since you don't dynamically generate code, you can offline generate >> these ELF files and redirect the symbol parser bits to that (we already >> look for debug ELF files in various locations), or... >> >> > The reason I went with this approach is because it is simple for >> > runtimes to implement and has no requirement that perf understand the >> > file format. I am open to feedback if there is a preferred solution >> > that would still work for older kernels as well. >> >> Since, someone somewhere needs to go parse this funny new file format >> anyhow to either generate /tmp files or fake ELF files or whatever, you >> might as well put that decoder in perf? >> If you have a new binary format, I think you'd have to write the parser in perf. >> Or just ship these fake ELF files in /usr/lib/debug/ or whatever the >> 'right' location for the distro at hand is. >> > > This seems like a reasonable approach. > > Stephane, are your changes available for public consumption? Last I > recall, the patches were still in review. > I will post V8 this week. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/